Police in Moscow and St. Petersburg have detained at least 68 people taking part in unauthorized protests against a criminal case filed against 10 Russians accused of extremism.

Several dozen protesters gathered outside the headquarters of the Federal Security Service (FSB) on Moscow's Lubyanka Square on October 28.

Police detained 18 of them as the demonstrators began a march in the center of capital.

Some 50 people were also detained during a demonstration in the center of St. Petersburg, including two journalists who were later released.

Small protests were held in other Russian cities and towns, including Rostov-on-Don in the south, Novosibirsk in Siberia, and Penza, some 600 kilometers southeast of Moscow.

The protests were held to support 10 defendants accused of extremism in a case over a group called New Greatness. Protesters believe the case was a provocation by the authorities.

The New Greatness defendants say they were participating in an online chat group critical of the government when one participant proposed creating a political movement.

It was later revealed that the person who proposed the idea, wrote the movement's charter, and rented premises for its gatherings was an agent of the FSB.

"I would never have believed that such a thing could happen to me and my child. And that means it could happen to anybody," said Julia Pavlikova, who says she is the mother of a girl charged in the case.

"One morning they knocked on the door and took away my child," she told the AFP news agency while protesting in Moscow.